1. Field of the Invention
The present invention relates to aluminum alloy-based extruded multi-path flat tubes for the heat exchanger, wherein the heat exchanger includes the flat tubes that are formed into a flat shape having multiple paths of fluid passage bores by performing the extruding operation, and may be constructed by joining those flat tubes with fins or header pipes by performing the brazing operation. The present invention also relates to a method of manufacturing such extruded multi-path flat tubes.
2. Prior Art
In general, the extruded multi-path flat tube that is used for the heat exchanger may be obtained by extruding the aluminum alloy billets and forming them into the flat shape, and the heat exchanger may be constructed by joining those flat tubes thus obtained with fins or header pipes by performing the brazing operation.
Of recent years, as demands arise for making the pipe or tube lighter or thinner or for permitting new types of coolants to be employed in the heat exchanger, a higher mechanical resistant strength is required for the extruded flat tubes that form a principal component of the heat exchanger in order to meet such demands. It may be understood, however, that the heat exchanger is constructed by joining the extruded flat tubes with other fins or header pipes by performing the brazing operation at the temperature of about 600° C. For the JIS 1XXX series alloys or Al—Mn series alloys that are used for the conventional extruded flat tubes, therefore, the mechanical resistant strength may become weakened during the brazing operation and the extruded flat tubes are actually used under the conditions in which they have the weakest mechanical resistant strength. For those recent years, therefore, studies are being made on the use of JIS 6XXX-series alloys that exhibit the comparatively good extrudability among other age-hardening alloys, in order to provide the higher mechanical resistant strength for the extruded flat tubes (see Japanese patent application now opened for the public examination under H5 (1993)-171328).
It should be noted, however, that those alloys contain Mg that may reduce the extrudability as compared with the other conventional alloys. It is thus practically impossible or difficult to extrude them into the flat tubes as required. Furthermore, Mg may react with Nocolok flux that is generally used for the brazing operation, which may reduce the brazability remarkably.